1. Field of the Invention
The present invention relates to an optical recording disk having a dye film as a recording layer and, more particularly, to a write-once type of optical recording disk using a phthalocyanine dye.
2. Prior Art
In recent years, optical recording disks of the write-once, rewritable (erasable) and other types have been of great interest as high capacity information carrying media. Some optical recording disks use a dye film as their recording layer. From a structural aspect, commonly used optical recording disks are classified into an air-sandwich structure type having an air space on a dye base recording layer and a close contact type having a reflective layer in close contact with a dye base recording layer. The latter has the advantage of enabling reproduction in accordance with the compact disk (CD) standard. For instance, reference is made to Nikkei Electronics, Jan. 23, 1989, No. 465, page 107; the Functional Dye Department of the Kinki Chemical Society, Mar. 3, 1989, Osaka Science & Technology Center; and Proceedings SPIE--The International Society for Optical Engineering, Vol. 1078, pp. 80-87, "Optical Data Storage Topical Meeting", 17-19, Jan. 1989, Los Angels.
Usually, the above-mentioned recording layer is formed by the coating of a dye coating solution on the substrate.
So far, cyanine dyes have mainly been studied as dyes used for recording layers. However, the cyanine dyes are generally less resistant to light, and is little reliable on recording when applied to recording layers. An attempt has thus been made at use of phthalocyanine dyes excellent in stability to light, heat, humidity and the like.
However, the phthalocyanine dyes are generally less soluble in organic solvents. When a recording layer is formed by use of a dye coating solution, therefore, it is difficult to prepare such a dye coating solution and, hence, to form a dye film of effective thickness.
It has thus been attempted to introduce substituents in the phthalocyanine dyes for solubilization.
For instance, JP-B 3-16916 discloses a phthalocyanine compound with five to sixteen alkoxy or aryloxy groups introduced therein as substituents and JP-A 5-25179 discloses a halogenated alkoxyphthalocyanine.
JP-B 3-16916 also teaches that toluene and the like are used as coating solvents. However, it is not preferable to use such aromatic hydrocarbon solvents, because they attack polycarbonate (PC) that is a commonly used substrate material.
On the other hand, the halogenated alkoxyphthalocyanine disclosed in JP-A 5-25179 is prepared through the steps of synthesizing alkoxyphthalocyanine and then halogenating it. A specific reaction solvent must be selected for the halogenation, and the amount of solvent, the reaction temperature and other parameters must be controlled as well. In other words, this compound is difficult to synthesis and low in yield.
It is thus desired to use a phthalocyanine dye which can be synthesized in a relatively ready manner and is well soluble in a solvent that is unlikely to attack a substrate material such as PC and is handled with ease, for instance, an alcoholic or aliphatic hydrocarbon type of organic solvent.
A primary object of this invention is to provide an optical recording medium including a recording layer of sufficient thickness and good-enough quality, which has been formed by use of a phthalocyanine dye that can be synthesized in a relatively ready manner, can be well handled because of being unlikely to attack a substrate material, and is well soluble in a coating solvent. This optical recording medium is so stable in performance that it can comply with the CD standard.